As a motor having high efficiency and a wide variable speed range, a permanent magnetic synchronous motor (PMSM), in particular, an interior permanent magnetic synchronous motor (IPMSM) in which a permanent magnet is embedded in a rotor has found extensive applications such as a compressor driving motor of an air conditioner for vehicle and a drive motor for electric automobile. Demand for the motor is expected.
A motor control device that controls driving of the motor of this type is composed of a motor, an inverter, a direct-current power supply, and a controller incorporating a microcomputer. In the motor, it is a common practice to use so-called sensorless control, which includes detecting an induced voltage of the motor from, for example, information concerning an electric current and a voltage detected by a controller and effectively detecting a rotor position θm to control the motor without using a physical sensor.
Concerning the sensorless control, there is disclosed a technique for periodically detecting a rotor position change amount Δθm using the detected rotor position θm, applying a predetermined filter to a value obtained by time-differentiating the rotor position change amount Δθm to calculate the number of revolutions ω of the rotor, i.e., the motor, setting a target voltage phase using the calculated number of revolutions ω, and calculating an inverter output frequency ω (the number of revolutions) using the rotor position change amount Δθm (see, for example, Patent Literature 1).